Q51615: C4056: Overflow in Constant Arithmetic

Article: Q51615
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 15-JAN-1990

The following code, when compiled at warning level 1 or greater,
causes the Microsoft C 5.10 optimizing compiler to produce warning
C4056:

   test.c(5) : warning C4056: overflow in constant arithmetic

This warning occurs because the compiler is reordering the addition of
the unsigned constants. This practice is no longer allowed according
to the ANSI standard.

To work around the problem, perform the arithmetic using long integer
constants where necessary (use 65535L rather than 65535u, for
example).

QuickC Versions 2.00 and 2.01 handle this code correctly because these
versions conform to more recent releases of the draft ANSI standard.

The following is the code that produces the error:

   void
   test ( unsigned dummy )
   {
       dummy = 65535u - (dummy - 1);
   }

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